Method and Apparatus for Breaking Rocks Field of Invention The present invention relates to a method of, and apparatus for, breaking rocks or substrate. The present invention finds particular utility in the mining, quarrying and demolition sectors, although is by no means limited thereto. Background It is known to use explosives and other energy intensive solutions to break and extract rock materials within mining, quarrying, demolition sectors. Explosives can also be used in related sectors, such as in the recycling of materials such as steel slag, often in the form of steel ‘skulls’ from electric arc furnaces, or other materials such as poorly cast concrete structures. This also helps in the collection and recycling of reinforcing steel from demolition activity. In mining or quarrying, it is conventional to use primary and secondary explosive charges. Typically, primary blasting is used to initially break the surface/structure of the rock, whilst secondary blasting is used to reduce in size large rocks resultant from the primary blasting. The use of explosives is dangerous. Secondary blasting is expensive and particularly dangerous. Often explosive charges from the primary blast have not ignited as such residual explosives are still in the rock structure. It would be advantageous to limit the explosive requirement in mining, quarrying or demolition. It would be particularly desirable to limit, or even avoid, using the secondary blasting whilst mining or quarrying. Disclosure of the Invention According to the present invention there is provided a method of breaking rock comprising mapping a surface of the rock to determine structural weaknesses, and targeting and impacting the structural weakness with a breaking tool. The present arrangement recognises the disparity between compression strength and tensile strength of rock. Compression strength is the capacity of a material or structure to withstand loads tending to reduce its size. This is to be compared with tensile strength, which withstands loads tending to elongate the material of structure. In other words, compressive strength resists compression (being pushed together), whereas tensile strength resists tension (being pulled apart). Rock strength is specified in terms of tensile strength and compressive strength (shear strength and impact strength may also be relevant, but have limited applicability to this arrangement). The tensile strength of rock (or rock-like material) is defined as the pulling force, required to rupture a rock sample, divided by the sample’s cross-sectional area. The tensile strength of rock (or rock-like material) can be very small and for some rock types can be of the order of 10% the compressive strength. Thus, a rock material is more likely to fail in tension than in compression. For most rocks, generally, the tensile strength of rock is around 25 – 30% of the compressional strength. In materials such as rock, structural weaknesses are typically cracks and/or block joints or seams. It is highly advantageous to be able to determine the position of the cracks, seams or block joints, and to be able to strike them consistently. Striking a weak point on the rock surface means the breaking force needs to overcome the rock’s tensile strength, rather than its compression strength. The present invention targets and impacts such structural weaknesses. Preferably, the mapping of the surface of the rock is achieved by detecting electromagnetic emissions from the rock. It is preferred that the mapping of the surface of the rock is achieved with thermal imaging, spectral imaging or hyper-spectral imaging. These methods may be used independently, or in any combination thereof. Typically, a rock structure will comprise water and air. Collectively, rock, water and air may be termed earth materials. The air and water content in the rock typically represents structural weaknesses. There are significant thermal heat capacity differences between rock, water and air. So when earth materials are energised they tend to emit electromagnetic radiation at different measurable values. The electromagnetic radiation is typically in the infra red range, and hence thermal imaging is particularly useful. Spectral and hyper-spectral imaging may supplement (or, in certain scenarios, replace) the mapping data as different substrate materials may be detectable in a wider EM spectrum. Rock typically comprises seams. Such seams may be chemically different to the majority of the rock, and may show up in a spectral scan. Preferably the mapping of the surface is updated periodically. It is highly desirable that an up-to- date database of the rock structure is maintained. It is preferred that an initial primary explosive blast is used. Such a blast typically energises the rock, and particularly the rock surface, so that the structural weaknesses (cracks, seams and the like) have enhanced visibility to spectral, and particularly thermal, imaging. However, it may be possible to rely on ambient radiation, such as solar energy, to produce a thermal image map. In areas of the extraction operation that are being heavily mined, where vehicles are already working, the vibrations of the vehicular movements and the working of the substrate with breaker technologies such as hydraulic hammers will add to the energy passing through the substrate adding to the friction within the cracks and hence changing their thermal profiles compared to the surrounding substrate mass. In such a scenario it would be advantageous to readily update the mapping scans. Preferably the thermal imaging map is periodically updated in areas of heavy vehicle use. It is preferred that a threshold is determined based on vehicle usage, with appropriate updating of the thermal map performed when the threshold is reached. Preferably the thermal imaging is allied with an existing scanning system. It is preferred that thermal or spectral mapping is performed in parallel with a topography scan. It is preferred that the topography scan is achieved with LiDAR. It is particularly preferred that the thermal scan and LiDAR scan form a composite image. A preferred arrangement would see a composite of a spectral, thermal and LiDAR scan. It is preferred that the thermal image is provided for a mining or quarrying site using one or more electromagnetic sensors mounted on one or more airborne vehicles. Such vehicles may be drones. It is further preferred that the thermal or spectral image is supplemented by additional sensors mounted on breaker vehicles, or additional ground based vehicles. It is particularly preferred that a combination of autonomous land-based and airborne vehicles is used. The present arrangement finds particular utility in breaking what are termed, in the mining, quarrying and demolition sectors, oversized rocks. Typically oversized rocks are freed from the main substrate by the primary blast of the explosives but are too large to be processed by conventional means. These oversized rocks would typically undergo secondary blasting. As mentioned, the tensile strength of rock is usually around 30% of its compressional strength. So if the cracks can be detected from a thermal picture, a breaking tool, rather than explosives, could be used. The thermal picture is used to allow the breaking tool to accurately strike the weak point of the oversized rock. According to a second aspect of the present invention there is provided a system to implement the method of breaking rock. Preferably, the system comprises a mapping sensor and a breaking tool. Advantageously the mapping sensor is a thermal sensor, a spectral sensor, or a combination of the two. It is preferred that the breaking tool is mounted on a mobile platform. It is preferred that the mobile platform is a vehicle. It is preferred that the breaking tool is a hydraulic hammer, or similar device. It is particularly preferred that the rock breaking tool uses an electrical drive that out accelerates gravity to deliver a high kinetic energy impact at a target point. Such an arrangement is advantageous in that it avoids detrimental vibration effects of traditional hydraulic hammers. Legacy hydraulic hammers operate at hundreds of impacts per minutes, so can be disadvantageous in that they have a tendency to reduce the operational lifespan of a carrier vehicle due to the resultant vibrations caused in use. As weak spots in the rock are targeted, fewer impacts on the rock are required to break the rock structure. A further advantage is that a less powerful breaking tool could be utilized to break the rock. Preferably the mobile platform is either autonomous or operated by remote control, although it is envisaged that the mobile platform could be operated by a driver. It is preferred that the mapping sensor is mounted on the vehicle with the breaking tool. However, it is equally preferred that the mapping sensor is mounted on a secondary vehicle. It is also envisaged providing multiple secondary vehicles for each breaker vehicle. In preferred embodiments the secondary vehicle is an airborne vehicle, such as a helicopter. In particularly preferred arrangements, the secondary vehicle is a drone. It is particularly preferred that a mixture of land-based vehicles and airborne vehicles are used. It is preferred that at least some of the vehicles are unmanned drones. In order that the present invention be more readily understood, specific embodiments will now be described with reference to the accompanying drawings. Description of drawings Figure 1a shows a schematic of a system operable to perform a method in accordance with the present invention. Figure 1b shows a schematic of a second system operable to perform a method in accordance with the present invention. Figure 2 shows an example of a vehicle mounted with a breaking tool. Description of Specific embodiments The present arrangement relates to improvements in mining, quarrying and demolition. The present arrangement seeks to enhance efficiency, to reduce production costs per tonne and improve safety in rock-type material extraction. Specifically, the arrangement provides guidance to consistently strike a target extraction sector resource material (such as a rock substrate) on a weak spot in its mass structure to optimize extraction or demolition. It is known to use of explosives and other energy intensive solutions to break and extract rock materials within the mining, quarrying and demolition industries. The explosives may be used in various stages; the first is typically called the primary blast, the second the secondary blast, and so on. However, the continued use of explosives is hazardous to safety, particularly with respect to the secondary (and subsequent) blast. Secondary blasting in the mining, quarrying and demolition sectors is often used on what are termed oversized rocks. Typically oversized rocks are freed from the main substrate by the primary blast of the explosives but are too large to be processed by conventional means. Such oversized rocks would normally undergo secondary blasting. Secondary blasting is expensive and can be particularly dangerous. All the explosive charge from a primary blast may not ignite. Accordingly, residual explosives may be contained in the rock. Such explosive can be detonated during the secondary blasting phase, with potentially hazardous results. It is thus advantageous to reduce the amount of explosive used. The tensile strength of rock or rock-like material is around 25 – 30% of its compressional strength. Accordingly, being able to exploit weak spots in a rock structure will more readily cause the rock to break about the weak point. Such an arrangement offers far better energy efficiency in a rock breaking enterprise. Weak spots in rock are primarily present as cracks and/or block joint or seams. It is thus advantageous to be able to strike the weak spots consistently. The present arrangement seeks to utilize one or a combination of thermal, spectral or hyper-spectral imaging to ascertain the location of weak spots. The present arrangement specifically looks to break rock using a focus mechanical method, rather than relying on explosives. Natural or man-made radiation cause cracks in rock surfaces to be detectable by sensors, normally in the infrared part of spectrum. This is because there are significant thermal heat capacity differences between earth materials such as water, rock and air. When such earth materials are energised they tend to emit electromagnetic (EM) radiation outputs at different measurable values. Accordingly, weak spots in the rock are readily visible in the IR range of the spectrum. Hyper-spectral analysis may reveal the location of cracks or seams, due to potential differences in chemical construction. Mining and quarry operations typically still rely on primary explosives blasting to break up the rock they are looking to extract. This is likely to be the case for the foreseeable future. The blast of the explosives sends significant energy through the substrate. Without wishing to be bound by theory, as the shock waves from the primary blast dissipate, that cracks already present and/or newly created cracks in the blasted substrate will rub against their respective internal sides causing fraction and convert the energy from the explosion to heat. The use of thermal or spectral imaging cameras allows said cracks to be represented on an imaging device, such as a monitor. Figure 1a shows an example system operable to perform a method in accordance with the present arrangement. Such an arrangement discloses a rock substrate 10 and a vehicle 12. The vehicle 12 comprises a breaking tool 14, and a thermal sensor 16. The breaking tool 14 may be a hydraulic hammer. However, it is more preferred that the breaking tool 14 is a high impact drive that out accelerates gravity to deliver a high kinetic energy impact. Typically, but not necessarily, the manned vehicle is moved into position to the rock substrate 10 at a mine, quarry or demolition site after a primary explosive blast. It may be possible to rely on ambient radiation from the sunlight on the site to provide an initial thermal plan of the rock structure. A driver of the vehicle 12 is provided access, typically via a monitor mounted within the vehicle 12, to visual data from EM sensors 16 that receive EM emissions from the rock substrate 10 subjected to the primary blast, and that is desirable to break. The cracks in the rock substrate 10 have a different thermal signature to the surrounding structure. This is particularly the case after a primary explosive blast. The thermal signature of the cracks allows the operator of the vehicle 12 to position the breaking tool 14 to deliver maximum impact (i.e. maximum energy transfer) to the crack in the target rock substrate 10. A high kinetic energy, single impact breaking tool 14 allows for all the energy of the breaking tool to be focused on the crack – the structural weakness – of the rock substrate 10. The breaking tool 14 striking the rock substrate 10 provides further energy into the rock, and thus representation shown on the monitor of the thermal image is updated. The initial strike, or strikes, if a hydraulic hammer is used, causes vibration in the cracks. Such vibrations can be used to supplement the thermal image map. Typically, the vehicles in mining or quarrying are large and heavy. Accordingly, the very presence of a vehicle on the site will cause local vibrations, adding to internal friction and heating in the local area cracks. Accordingly, it is possible to periodically update the thermal image map; even if no further explosive blasts are used. Such an arrangement allows for precision striking at determined weak points in the rock substrate 10. Even if a high-impact breaker tool is used, in reality multiple strikes may be required. However, if the EM emissions map is updated with sufficient frequency, the strike point can, if appropriate, be adjusted between each strike. Such adjustments may be minor, but the present arrangement ensures that each strike is precisely on the targeted weak point of the rock substrate. A further preferred arrangement provides a remote-operated land vehicle. An operator is able to control the vehicle from a remote position. In this arrangement, the remote position will have a monitor (or similar) to display the thermal image provided from the EM sensors. The remote operator is operable to manoeuvre the vehicle to a location that the output from the EM sensors designate that there is a crack, joint or other weak spot. The arrangement also provides for additional vehicles comprising sensor systems, but without breakers. Such scout vehicles are beneficial in that they are operable to record and provide data to an overall site map. It will be appreciated that such scout vehicles may be land-based, or may be airborne. For example, one or more drones may advantageously have thermal imaging cameras mounted thereon. Such an arrangement would allow for a large area to be thermally mapped. The use of a combination of drones and scout vehicles is particularly advantageous. The drones are able to capture a thermal image over a wide area, with the scout vehicles supplementing the thermal map in areas of interest. Figure 1b shows such an arrangement. Here, there is provided a rock substrate 10 and a vehicle 12. The vehicle 12 comprises a breaking tool 14, and a thermal sensor 16. The breaking tool 14 may be a hydraulic hammer. However, it is more preferred that the breaking tool 14 is a high impact drive that out accelerates gravity to deliver a high kinetic energy impact. A drone 18 is provided, and may have mounted thereon a spectral or thermal mapping system. A combination may be used. It is preferred that the present arrangement is operable to be allied with existing systems. Such integration would allow for efficient incorporation on the present arrangement. Present quarrying and mining operations are increasingly relying on digital solutions, mainly to map resource and increasingly to develop local Wi-Fi or positioning system knowledge for next generation sites. There is also a move towards use of autonomous vehicles for extraction and/or logistics of resource removal for onward processing of material after breaking. This is mapping not looking for weak spots and cracks but to estimate a resource present and to give a site positioning system to enhance the removal and its process of extracting material. The mapping of these extraction sites is typically done with LiDAR or other 2D or 3D camera solutions. Typically, LiDAR sensors are mounted on a drone to allow the site to be scanned. Thermal imaging sensors could be mounted in parallel with said LiDAR sensors. The output from both sensors could readily be used to ensure that readily accessible weak spots in the rock substrate are tackled first. Digital site coverage is desirably performed in the timeliest manner, for example after each firing of site explosives, or after recording a new or updated heat signature and/or LiDAR map of the site. Any cracks in the rocks then will reveal themselves more clearly due to the vibrations caused by the explosion, recording in the infra red part of the EM spectrum. It is particularly desirable to always have an up-to-date scan of the rock substrate. As explosives or rock breakers are used, the location, or more likely, the amount of weak spots, may vary. The thermal map or composite thermal and LiDAR map of the site may be updated digitally with each explosive firing event to continuously improve site knowledge of the cracks in the target resource substrate. Future extraction operations are moving towards autonomous vehicles and autonomous general site operations. It is thus preferred that the site’s thermal signature, preferably together with a LiDAR map, is created and digitally recorded for new or potential sites, to allow analysis of the locations of cracks and/or joints. In order to further reduce the amount of explosive required, potential sites could be mapped using solar heating, or other natural EM emissions detectable from chemical make-up of substrate by hyper-spectral analysis. A site that shows promise could then be subjected to a primary explosive blast and the site then subjected to a further thermal (and potentially LiDAR) scan to determine a fuller understanding of the weak areas on the site. Preferably the electromagnetic emissions digital map may be continuously updated, potentially added to by machine learning algorithms to recognise cracks and joints and how they propagate. Such an arrangement may be material specific. The digital mapping and recording of the site will allow an accurate positioning system to guide a vehicle, autonomous, or driven or remote driven, to the location of a weak point, such as a crack or joint, in the substrate. The present arrangement may be multi-layered, with secondary vehicles carrying out an initial thermal scan of a site. This may be a primary guidance to manoeuvre a breaker vehicle to the rock or substrate of interest. The breaker vehicle would preferably comprise on-board EM sensors for detection of infra-red. Figure 2 shows an example of a typical breaker vehicle. As a secondary scan, said EM sensors are arranged to supplement data to the overall site digital map created to enhance detection and location of cracks / joints. Accordingly, the breaker vehicle comprises its own guidance system to allow the vehicle to place its breaking tool as accurately as possible onto the crack/ weak-point / joint in the substrate. The guidance system on the vehicle works in tandem with a site-wide thermal imaging system by providing detailed feedback of smaller area into the overall digital site map. The above specific embodiments are provided by way of reference only. Many modifications and variations are covered by the appended claims.